Ray Allen to start for Avery Bradley

BOSTON -- Celtics second-year shooting guard Avery Bradley will miss Monday's Game 5 due to shoulder issues, which will force Ray Allen back into the starting lineup for a pivotal battle with the Philadelphia 76ers in the teams' Eastern Conference semifinal series at TD Garden.

Bradley dislocated his left shoulder for the third time this postseason during Friday's Game 4 loss and despite the additional time off, he's not ready to get back on the floor. Compounding matters, he's now experiencing discomfort in his right shoulder, something Rivers believes could be from him compensating for the sore left rotator cuff.

"It's not just the one, it's actually both shoulders," Rivers said. "That's probably from trying to protect the other one. It's pretty bad. Now -- we've got to keep winning, obviously -- he'll still play games, I think. I think this is probably how it's going to be from this point on. He'll play a game, miss a couple, play a game. That's the way it'll be."

Pressed on his availability moving forward, including Wednesday's Game 6, Rivers was noncommittal.

"I don't know," he said. "We're going to focus on tonight. Take care of that, then obviously tomorrow we'll worry about that. We just have to focus on tonight."

What do the Celtics lose without Bradley on the floor?

"Well, we lose our defensive captain, really -- him and Kevin (Garnett)," Rivers said. "They are both terrific. And without Avery at guard, it takes away the ability to put Rondo on different guys to give him a rest at times. I think ball pressure against Philly is really important and to ask Rondo to do that and run the team is very difficult. It clearly takes something out of our lineup."

Rivers said the team will lean on a three-man system of Allen, Mickael Pietrus and Keyon Dooling to cope with the loss of Bradley. He's hoping one of the three will step up and carry the load in Bradley's absence.

"One of the three -- Keyon, Ray or MP -- will take a bigger role without Avery," said Rivers. "It'd be easy to tell you before the game who it would be. Obviously, you hope it's Ray, but Ray is limited with his health, it may end up having to be one of the other two guys."

Allen, who has appeared as a reserve all eight games this postseason and hasn't started since April 4, said he doesn't think it'll be hard to jump back in the starting lineup.

"How does it change? I mean, I've started here for five years. It's not like I'm foreign to the situation," Allen said. "We play like we've always played. We've won a lot of games with that lineup, so we'll just click right in."

Of course, one thing does change: Allen has been sneaking back to the locker room during starting lineup introductions to use the bathroom at times since moving to a reserve.

"I won't be doing that tonight," he said.

Jackie MacMullan and Greg Payne contributed.